Piezoelectric ceramics, manufacturing method therefor, piezoelectric element, liquid discharge head, ultrasonic motor, and dust removal device

ABSTRACT

Provided are a barium titanate-based piezoelectric ceramics having satisfactory piezoelectric performance and a satisfactory mechanical quality factor (Q m ), and a piezoelectric element using the same. Specifically provided are a piezoelectric ceramics, including: crystal particles; and a grain boundary between the crystal particles, in which the crystal particles each include barium titanate having a perovskite-type structure and manganese at 0.04% by mass or more and 0.20% by mass or less in terms of a metal with respect to the barium titanate, and the grain boundary includes at least one compound selected from the group consisting of Ba 4 Ti 12 O 27  and Ba 6 Ti 17 O 40 , and a piezoelectric element using the same.

TECHNICAL FIELD

The present invention relates to a piezoelectric ceramics, amanufacturing method therefor, a piezoelectric element, a liquiddischarge head, an ultrasonic motor, and a dust removal device.Specifically, the present invention relates to a barium titanate-basedpiezoelectric ceramics provided with satisfactory piezoelectricperformance and a satisfactory mechanical quality factor (Q_(m)) bycontrolling composition of a crystal grain boundary and a crystalstructure.

BACKGROUND ART

A commonly used piezoelectric ceramics is an ABO₃-type perovskite oxidesuch as lead titanate zirconate (hereinafter, referred to as “PZT”).

However, it is considered that PZT, which contains lead as an A-siteelement, may cause environmental problems. Therefore, a piezoelectricceramics with a lead-free perovskite-type oxide has been desired.

Barium titanate is known as a material for a lead-free perovskite-typepiezoelectric ceramics. Patent Literature 1 discloses barium titanateprepared by a resistance heating/two-step sintering technique. Thepatent literature describes that a ceramics with excellent piezoelectricproperty can be obtained when nano-sized barium titanate powder issintered by the two-step sintering technique. However, the ceramicsobtained by the two-step sintering technique is not suitable for use ina resonance device because it has a small mechanical quality factor andlow high-temperature durability.

Further, Patent Literature 2 discloses a ceramics obtained by replacingpart of a barium site in barium titanate with calcium and further addingmanganese, iron, or copper. The patent literature describes that theceramics has an excellent mechanical quality factor by virtue ofmanganese, iron, or copper. However, an increase in calcium contentshifts the temperature of crystal phase transition to about −50° C.,resulting in a remarkable decrease in piezoelectric performance.

Further, it is well known in the art that an increase in amount ofmanganese added leads to precipitation of manganese oxide (MnO_(x))outside crystal particles of barium titanate. The manganese oxide lacksproperties of a dielectric substance, and hence causes a decrease inpiezoelectric performance of a ceramics. Further, the manganese oxidecauses a decrease in mechanical quality factor because the valence ofmanganese is unstable.

In other words, a barium titanate-based piezoelectric ceramics isexpected to have both of satisfactory piezoelectric performance and ahigh mechanical quality factor.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent Application Laid-Open No. 2008-150247-   PTL 2: Japanese Patent Application Laid-Open No. 2010-120835

SUMMARY OF INVENTION Technical Problem

The present invention has been made to cope with the above-mentionedproblems. An object of the present invention is to provide apiezoelectric ceramics provided with satisfactory piezoelectricperformance and a satisfactory mechanical quality factor (Q_(m)) bycontrolling composition of a crystal grain boundary and a crystalstructure, and a manufacturing method therefor.

Another object of the present invention is to provide a piezoelectricelement, a liquid discharge head, an ultrasonic motor, and a dustremoval device each using the piezoelectric ceramics.

Solution to Problem

A piezoelectric ceramics for solving the above-mentioned problemsincludes: crystal particles; and a grain boundary between the crystalparticles, in which, the crystal particles each include barium titanatehaving a perovskite-type structure and manganese at 0.04% by mass ormore and 0.20% by mass or less in terms of a metal with respect to thebarium titanate, and the grain boundary includes at least one compoundselected from the group consisting of Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀.

A manufacturing method for a piezoelectric ceramics for solving theabove-mentioned problems includes at least: producing granulating powderby adding a binder to barium titanate particles each including manganeseat 0.04% by mass or more and 0.20% by mass or less in terms of a metal;and sintering a mixture prepared by adding at least one compoundselected from the group consisting of Ba₄Ti₁₂O₂₇ particles andBa₆Ti₁₇O₄₀ particles to the granulating powder.

Further, a manufacturing method for a piezoelectric ceramics for solvingthe above-mentioned problems includes at least: producing granulatingpowder by adding a binder to barium titanate particles each includingmanganese at 0.04% by mass or more and 0.20% by mass or less in terms ofa metal; and sintering a mixture prepared by adding titanium oxideparticles each having an average particle diameter of 100 nm or less tothe granulating powder.

A piezoelectric element for solving the above-mentioned problemsincludes at least: a first electrode; a piezoelectric ceramics; and asecond electrode, in which the piezoelectric ceramics includes theabove-mentioned piezoelectric ceramics.

A liquid discharge head for solving the above-mentioned problems is aliquid discharge head, using the above-mentioned piezoelectric element.

An ultrasonic motor for solving the above-mentioned problems is anultrasonic motor, using the above-mentioned piezoelectric element.

A dust removal device for solving the above-mentioned problems is a dustremoval device, using the above-mentioned piezoelectric element.

Advantageous Effects of Invention

According to the present invention, it is possible to provide thepiezoelectric ceramics provided with satisfactory piezoelectricperformance and a satisfactory mechanical quality factor (Q_(m)) bycontrolling composition of a crystal grain boundary and a crystalstructure, and a manufacturing method therefor. Further, according tothe present invention, it is possible to provide the piezoelectricelement, the liquid discharge head, and the ultrasonic motor each usingthe piezoelectric ceramics.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic diagram illustrating an embodiment of theconstruction of a liquid discharge head of the present invention.

FIG. 1B is a schematic diagram illustrating an embodiment of theconstruction of the liquid discharge head of the present invention.

FIG. 2A is a schematic diagram illustrating an embodiment of theconstruction of an ultrasonic motor of the present invention.

FIG. 2B is a schematic diagram illustrating an embodiment of theconstruction of the ultrasonic motor of the present invention.

FIG. 3A is a schematic diagram illustrating an embodiment of a dustremoval device of the present invention.

FIG. 3B is a schematic diagram illustrating an embodiment of the dustremoval device of the present invention.

FIG. 4A is a schematic diagram illustrating the construction of apiezoelectric element of the present invention in each of FIGS. 3A and3B.

FIG. 4B is a schematic diagram illustrating the construction of thepiezoelectric element of the present invention in each of FIGS. 3A and3B.

FIG. 4C is a schematic diagram illustrating the construction of thepiezoelectric element of the present invention in each of FIGS. 3A and3B.

FIG. 5 is pattern diagram illustrating a vibration principle of a dustremoval device of the present invention.

FIG. 6 is a conceptual diagram illustrating an embodiment of apiezoelectric ceramics of the present invention.

FIG. 7A is an SEM secondary electron image of a surface of apiezoelectric ceramics of the present invention.

FIG. 7B is a TEM observation image of the piezoelectric ceramics of thepresent invention.

FIG. 8A is a [100] incident electron diffraction pattern of Ba₄Ti₁₂O₂₇calculated from literature data.

FIG. 8B is an electron diffraction image of a non-perovskite-typestructure in the grain boundary of a piezoelectric ceramics of thepresent invention.

FIG. 9A is a [011] incident electron diffraction pattern of Ba₆Ti₁₇O₄₀calculated from literature data.

FIG. 9B is an electron diffraction image of the non-perovskite-typestructure in the grain boundary of a piezoelectric ceramics of thepresent invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention are described.

A piezoelectric ceramics according to the present invention includes:crystal particles; and a grain boundary between the crystal particles,in which, the crystal particles each include barium titanate having aperovskite-type structure and manganese at 0.04% by mass or more and0.20% by mass or less in terms of a metal with respect to the bariumtitanate, and the grain boundary includes at least one compound selectedfrom the group consisting of Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀.

The term “ceramics” used herein refers to an aggregate (also referred toas bulk) of crystal particles sintered by thermal treatment, or theso-called polycrystal, in which the main component thereof is a metaloxide. The term also includes one processed after sintering. However,the term does not include any powder or powder-dispersed slurry.

The barium titanate having a perovskite-type structure is BaTiO₃. Inaddition, here, the barium titanate may include otherproperty-regulating components and impurities due to production as wellas manganese.

In the piezoelectric ceramics in the present invention, the compoundhaving a non-perovskite structure is present in the grain boundary ofcrystal particles outside the crystal particles of the barium titanatehaving a perovskite-type structure. The compound having a non-perovskitestructure is at least one compound selected from Ba₄Ti₁₂O₂₇ andBa₆Ti₁₇O₄₀.

Further, in this description, at least one compound selected fromBa₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ present outside the crystal particles isreferred to as “sub-particles.”

The Ba₄Ti₁₂O₂₇ belongs to a space group C2/m and has properties of adielectric substance. In addition, the Ba₆Ti₁₇O₄₀ belongs to a spacegroup A2/a and has properties of a dielectric substance.

The term “grain boundary” used herein refers to an interface betweencrystal particles (the interface includes cases where the crystalparticles are in contact with each other linearly and intermittently).Further, in the following description, among the “grain boundaries,” aplane or a line on which two crystal particles come into contact witheach other may be referred to as “boundary.” In addition, in thefollowing description, among the “grain boundaries,” a site at whichthree or more crystal particles cross with each other at one point or ona line may be referred to as “triple point” (three needle crystalparticles may cross with each other with a “line” in the boundary).

FIG. 6 is a conceptual diagram illustrating an embodiment of thepiezoelectric ceramics of the present invention and schematicallyrepresents a relationship among crystal particles, grain boundaries, andsub-particles. Barium titanate crystal particles are represented by 401.The crystal particles are in contact with each other via at least one ofa boundary and a triple point. The boundary between the crystalparticles is represented by 402 and the triple point is represented by403. A sub-particle present in the boundary between the crystalparticles is represented by 404. In the piezoelectric ceramics of thepresent invention, at least one compound selected from sub-particles,Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀, is present in the grain boundary (boundary ortriple point) of the crystal particles. In the figure, at least onesub-particle of Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ present at the triple point isrepresented by 405 or 406.

As one of techniques for easily distinguishing between the crystalparticle and the sub-particle, there is known a method using a scanningelectron microscope (SEM). In other words, the method utilizes a factthat observation of the surface of the piezoelectric ceramics by an SEMsecondary electron image allows a user to observe the crystal particleand the sub-particle with different contrasts.

FIG. 7A is an SEM secondary electron image obtained by observing thesurface of the piezoelectric ceramics of the present invention. Theimage reveals that a sub-particle present at a triple point 502 and acrystal particle 501 can be observed with different contrasts. Inaddition, FIG. 7B is an image of part of the piezoelectric ceramics,which includes the sub-particle, obtained by transmission electronmicroscopy (TEM). It is found that the TEM observation can distinguishthe part of a sub-particle 504 and the part of a crystal particle 503.

A barium (Ba) site of the barium titanate (BaTiO₃) may be partiallyreplaced with another bivalent metal or a pseudo-bivalent metal.Examples of the bivalent metal, with which the Ba site can be replaced,include Ca and Sr. Examples of the pseudo-bivalent metal, with which theBa site can be replaced, include (Bi_(0.5)Na_(0.5)), (Bi_(0.5)K_(0.5)),(Bi_(0.5)Li_(0.5)), (La_(0.5)Na_(0.5)), (La_(0.5)K_(0.5)), and(La_(0.5)Li_(0.5)). A replacement ratio in the case of partiallyreplacing the Ba site with another bivalent metal or a pseudo-bivalentmetal is 20 atm % or less, preferably 10 atm % or less. When thereplacement ratio exceeds 20 atm %, high piezoelectric property inherentto barium titanate may not be sufficiently obtained.

A titanium (Ti) site of the barium titanate (BaTiO₃) may be partiallyreplaced with another tetravalent metal or a pseudo-tetravalent metal.Examples of the tetravalent metal, with which the Ti site can bereplaced, include Zr, Hf, Si, Sn, and Ge. Examples of thepseudo-tetravalent metal, with which the Ti site can be replaced,include a combination of a divalent metal and a pentavalent metal (M²⁺_(1/3)M⁵⁺ _(2/3)), a combination of a trivalent metal and a pentavalentmetal (M³⁺ _(1/2)M⁵⁺ _(1/2)), and a combination of a trivalent metal anda hexavalent metal (M³⁺ _(2/3)M⁶⁺ _(1/3)).

In the piezoelectric ceramics of the present invention, a crystalparticle contains manganese in the range of 0.04% by mass or more and0.20% by mass or less, preferably 0.05 by mass or more and 0.17% by massor less in terms of a metal with respect to barium titanate. When apiezoelectric ceramics containing barium titanate as a main componentcontains a manganese component in the above-mentioned range, thepiezoelectric ceramics can be provided with improved insulating propertyand an improved mechanical quality factor (Q_(m)). When the content ofmanganese is less than 0.04% by mass with respect to the bariumtitanate, the mechanical quality factor of the piezoelectric ceramicscannot be sufficiently enhanced. In contrast, when the content ofmanganese is more than 0.20% by mass, hexagonal barium titanate or animpurity phase, which has less piezoelectric performance, may coexist.Thus, the piezoelectric performance of the entire piezoelectric ceramicsmay become insufficient.

Ba₄Ti₁₂O₂₇ or Ba₆Ti₁₇O₄₀, which is a compound constructing asub-particle included in the grain boundary, can be specified, forexample, by subjecting the compound to a comparison between adiffraction image obtained by a selected-area diffraction method using atransmission electron microscope (TEM) and data in a known literature.

The selected-area diffraction method is a method of observing adiffraction pattern of only a specific area in an enlarged imageobserved with a transmission electron microscope (TEM). The use of themethod allows the observation of only the diffraction pattern generatedfrom the above-mentioned compound.

The sub-particle can fill a void that may be formed in the grainboundary between crystal particles. When the void is filled with thesub-particle formed of at least one of the dielectric substances,Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀, the dielectric constant of the piezoelectricceramics can be enhanced compared with that in a state in which the voidexists. In other words, the filling of the void with the sub-particlecan enhance the piezoelectric performance of the piezoelectric ceramics.

In the piezoelectric ceramics of the present invention, it is desiredthat the ratio of the at least one compound selected from the groupconsisting of Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ in the grain boundary whenobserved on one of a surface and a cross-section of the piezoelectricceramics be 0.05% by area or more and 1% by area or less, preferably0.1% by area or more and 0.5% by area or less with respect to the totalarea of one of the surface and the cross-section of the piezoelectricceramics.

When the content of Ba₄Ti₁₂O₂₇ or Ba₆Ti₁₇O₄₀ in the grain boundary, orthe ratio of the sub-particle in the whole piezoelectric ceramics isless than 0.05% by area, the precipitation of manganese oxide in thegrain boundary may not be completely prevented. Thus, high piezoelectricperformance inherent to barium titanate may not be sufficientlyobtained. When the ratio of the sub-particle in the grain boundary ismore than 1% by area, a sub-particle which has no piezoelectric propertyis excessively precipitated in the grain boundary. Thus, highpiezoelectric performance inherent to barium titanate may not besufficiently obtained.

Further, the ratio of the sub-particle included in the grain boundarywith respect to the piezoelectric ceramics can be calculated by theabove-mentioned method using a scanning electron microscope. The surfaceor cross-section of the piezoelectric ceramics containing manganese isobserved using a reflected electron image of the scanning electronmicroscope. In the above-mentioned observation method, the sub-particleand the crystal particle of the piezoelectric ceramics are observed withdifferent contrasts. Thus, the sub-particle is distinguished from thecrystal particle of the piezoelectric ceramics, and the ratio of thesub-particle is calculated by measuring the area ratio of both theparticles.

In the piezoelectric ceramics of the present invention, it is preferredthat the grain boundary includes: one of Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀; andthe Ba₄Ti₁₂O₂₇ and the Ba₆Ti₁₇O₄₀ both include manganese.

In general, the addition of manganese to a piezoelectric ceramics doesnot always lead to the presence of all the manganese added in the insideof crystal particles. When manganese is added to a conventionalpiezoelectric ceramics, the manganese added is present as manganeseoxide (MnOx) in the grain boundary.

In the piezoelectric ceramics that contains the manganese oxide in thegrain boundary, the manganese oxide, which does not have properties of adielectric substance, causes a decrease in insulating property of thepiezoelectric ceramics, resulting in a decrease in piezoelectricperformance as well. Further, the manganese oxide is present in thegrain boundary, or outside the crystal particles, causing the valence ofmanganese unstable. Therefore, the manganese oxide reduces a mechanicalquality factor of the piezoelectric ceramics.

In contrast, in the piezoelectric ceramics of the present invention, asub-particle, or at least one compound selected from Ba₄Ti₁₂O₂₇ andBa₆Ti₁₇O₄₀ is present in the grain boundary.

As Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ are dielectric substances, the presence ofsuch compounds in the grain boundary do not cause a decrease ininsulating property of the piezoelectric ceramics. Further, a state inwhich no manganese oxide is present in the grain boundary can beestablished by incorporating manganese, which has been present in thegrain boundary as manganese oxide, into the sub-particle. As a result,the decreases in piezoelectric performance and in mechanical qualityfactor due to manganese oxide described above can be prevented.

Therefore, in the piezoelectric ceramics of the present invention,Ba₄Ti₁₂O₂₇ or Ba₆Ti₁₇O₄₀ included in the grain boundary preferablycontains manganese.

In the piezoelectric ceramics of the present invention, it is desiredthat the content of manganese in at least one compound selected from thegroup consisting of Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ in the grain boundary be0.6% by mass or more and 2.8% by mass or less, preferably 1.0% by massor more and 2.0% by mass or less in terms of a metal with respect to theat least one compound selected from the group consisting of Ba₄Ti₁₂O₂₇and Ba₆Ti₁₇O₄₀.

When the content of manganese is less than 0.6% by mass, or the amountof manganese dissolved as a solid solution in at least one of Ba₄Ti₁₂O₂₇and Ba₆Ti₁₇O₄₀ is small, manganese, which is not dissolved as a solidsolution in the crystal particle, may cause precipitation of a compoundcontaining manganese as a main component, such as manganese oxide, inthe grain boundary.

Further, when the content of manganese is more than 2.8% by mass, or theamount of manganese dissolved as a solid solution in at least one ofBa₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ is large, the amount of the manganesedissolved as a solid solution in the crystal particle decreases. Thus,the piezoelectric ceramics may not be sufficiently provided withsufficient mechanical quality factor.

The content of the manganese may be specified, for example, from ananalytical result obtained by energy dispersive spectroscopy on an areawhere a crystal structure is defined on any of Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀when the grain boundary is observed by the selected-area diffractionmethod.

In the piezoelectric ceramics of the present invention, it is preferredthat the grain boundary includes Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀; and theBa₄Ti₁₂O₂₇ and the Ba₆Ti₁₇O₄₀ each include manganese.

When the grain boundary is occupied by Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀, thedielectric constant of the whole piezoelectric ceramics is increased,leading to an increase in piezoelectric performance. In addition,manganese dissolved as a solid solution in the crystal particle ofBa₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ can be prevented from being precipitated inthe grain boundary or void between the crystal particles as a compoundcontaining Mn as a main component such as manganese oxide (MnO).

In the piezoelectric ceramics of the present invention, it is preferredthat the content ratio of manganese in the Ba₄Ti₁₂O₂₇ be larger than thecontent ratio of manganese in the Ba₆Ti₁₇O₄₀. The content ratio ofmanganese in each of Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ can be evaluated, forexample, by a combination of energy dispersive spectroscopy with acrystal structure determined by the above-mentioned selected-areadiffraction method.

A large content of manganese in Ba₄Ti₁₂O₂₇ leads to increases ininsulating property and sintering density.

The term “particle diameter” of the piezoelectric ceramics used hereinrefers to the so-called “projected area diameter” in microscopicobservation, and refers to the diameter of a perfect circle having anarea equal to the projected area of a crystal particle. In the presentinvention, a measuring method for the particle diameter is notparticularly limited. For example, the particle diameter may bedetermined by image processing on a photographic image of the surface ofthe piezoelectric ceramics captured by a polarizing microscope orscanning electron microscope. An exemplary magnification in determiningthe particle diameter of the crystal particle is about 5 to 5,000 times.One of a light microscope and an electron microscope may be usedproperly depending on the magnification. The particle diameter may alsobe determined from an image of a ground surface or a cross-section ofthe ceramics instead of the surface thereof.

Next, a manufacturing method for a piezoelectric ceramics of the presentinvention is described.

A first aspect of the manufacturing method for a piezoelectric ceramicsaccording to the present invention includes at least: producinggranulating powder by adding a binder to barium titanate particles eachincluding manganese at 0.04% by mass or more and 0.20% by mass or lessin terms of a metal; and sintering a mixture prepared by adding at leastone compound selected from the group consisting of Ba₄Ti₁₂O₂₇ particlesand Ba₆Ti₁₇O₄₀ particles to the granulating powder.

The barium titanate particles each including manganese may include otherproperty-regulating components and impurities due to synthesis as wellas barium titanate and manganese. Examples of the impurities includecomponents derived from metals such as aluminum, calcium, niobium, iron,and lead, glass components, and hydrocarbon-based organic components.The content of the impurities is preferably 5% by mass or less, morepreferably 1% by mass or less.

The average particle diameter of the barium titanate particles eachincluding manganese as primary particles is not particularly limited.However, in order to obtain a high-density homogeneous piezoelectricceramics, it is desired that the average particle diameter of theprimary particles be 5 nm or more and 300 nm or less, preferably 50 nmor more and 150 nm or less. The density of the ceramics after sinteringmay become insufficient when the average particle diameter of theprimary particles is too small or too large. Here, the term “primaryparticle” refers to the minimum unit of a substance which can be clearlydistinguished from others among particles constructing powder. Theprimary particles may aggregate to form larger secondary particles. Thesecondary particles may be intentionally formed by a granulation stepusing a polymeric binder.

A manufacturing method for the barium titanate particles each includingmanganese and a manufacturing method for granulating powder includingadding a binder to the barium titanate particles each includingmanganese are not particularly limited.

In the case of manganese-attached barium titanate, the attaching may beperformed by adding a manganese component to commercially available orsynthesized barium titanate particles in a downstream step. An additionmethod for the manganese component is not limited. However, it isdesired that the manganese component be uniformly attached to thesurface of barium titanate. In the viewpoint, the most preferredaddition method is a spray-drying method. The spray-drying method isalso preferred from the viewpoints that the method allows producinggranulating powder by adding a binder concomitantly with the attachingof the manganese component and that the method allows making theparticle diameter more uniform.

In the case of barium titanate in which manganese is dissolved as asolid solution, a barium titanate precursor in which a manganesecomponent is previously incorporated may be crystallized. For example,an equimolar mixture of a barium compound and a titanium compound isprepared, and a desired amount of a manganese component is then added tothe mixture.

Subsequently, the mixture is calcined at about 1,000° C. to obtainbarium titanate particles in each of which the manganese component isdissolved as a solid solution.

Also in this case, a manufacturing method for the granulating powder isnot particularly limited. However, a spray-drying method is preferredfrom the viewpoint that the method allows making the particle diametermore uniform.

Examples of the binder which may be used in granulation includepolyvinyl alcohol (PVA), polyvinyl butyral (PVB), and an acrylic resin.The amount of the binder added is preferably 1% by mass to 10% by mass,more preferably 2% by mass to 5% by mass from the viewpoint of anincrease in density of a molded article.

Examples of the barium compound which may be used in the production ofthe barium titanate particles each including manganese include bariumcarbonate, barium oxalate, barium oxide, barium acetate, barium nitrate,barium aluminate, and various barium alkoxides.

Examples of the titanium compound which may be used for the bariumtitanate particles each including manganese include titanium oxide.

Examples of the manganese component which may be used for the bariumtitanate particles each including manganese include manganese compoundssuch as manganese oxide, manganese dioxide, manganese acetate, andmanganese carbonate.

In the piezoelectric ceramics obtained by sintering a mixture preparedby adding at least one of Ba₄Ti₁₂O₂₇ particles and Ba₆Ti₁₇O₄₀ particlesto the granulating powder, at least one of the Ba₄Ti₁₂O₂₇ particles andthe Ba₆Ti₁₇O₄₀ particles added is precipitated in the grain boundary. Bythe above-mentioned mechanism, such piezoelectric ceramics is capable ofkeeping Mn in the crystal particles to satisfy both the piezoelectricperformance and the mechanical quality factor. The addition amount ofeach of the Ba₄Ti₁₂O₂₇ particles and the Ba₆Ti₁₇O₄₀ particles ispreferably 0.02% by mass or more and 1.5% by mass or less. In otherwords, the manufacturing method A allows the Ba₄Ti₁₂O₂₇ particles or theBa₆Ti₁₇O₄₀ particles to be precipitated in the grain boundary withoutfail.

The mixed barium titanate particles are molded into a desired shape andthen sintered to give a ceramics.

A sintering method for the ceramics in the above-mentioned manufacturingmethod is not limited. Examples of the sintering method include electricfurnace sintering, energization heating, microwave sintering, millimeterwave sintering, and hot isostatic press (HIP).

The sintering temperature of the ceramics in the above-mentionedmanufacturing method is not limited, but is desirably a temperature thatallows the sufficient crystal growth of barium titanate. Thus, thesintering temperature is preferably 1,000° C. or more and 1,450° C. orless, more preferably 1,300° C. or more and 1,400° C. or less. Thebarium titanate ceramics sintered in the above-mentioned temperaturerange shows satisfactory piezoelectric performance.

In order to keep constant the properties of the piezoelectric ceramicsobtained by sintering with high reproducibility, it is preferred thatthe sintering be performed for about 1 hour or more and 12 hours or lesswhile keeping the sintering temperature constant in the above-mentionedrange.

A second aspect of the manufacturing method for a piezoelectric ceramicsaccording to the present invention includes at least: producinggranulating powder by adding a binder to barium titanate particles eachincluding manganese at 0.04% by mass or more and 0.20% by mass or lessin terms of a metal; and sintering a mixture prepared by adding titaniumoxide particles each having an average particle diameter of 100 nm orless to the granulating powder.

The barium titanate particles each including manganese may include otherproperty-regulating components and impurities due to synthesis as wellas barium titanate and manganese. Examples of the impurities includecomponents derived from metals such as aluminum, calcium, niobium, iron,and lead, glass components, and hydrocarbon-based organic components.The content of the impurities is preferably 5% by mass or less, morepreferably 1% by mass or less.

The average particle diameter of the barium titanate particles eachincluding manganese as primary particles is not particularly limited.However, in order to obtain a high-density homogeneous piezoelectricceramics, it is desired that the average particle diameter of theprimary particles be 5 nm or more and 300 nm or less, preferably 50 nmor more and 150 nm or less. The density of the ceramics after sinteringmay become insufficient when the average particle diameter of theprimary particles is too small or too large. Here, the term “primaryparticle” refers to the minimum unit of a substance which can be clearlydistinguished from others among particles constructing powder. Theprimary particles may aggregate to form larger secondary particles. Thesecondary particles may be intentionally formed by a granulation stepusing a polymeric binder.

A manufacturing method for the barium titanate particles each includingmanganese and a manufacturing method for granulating powder includingadding a binder to the barium titanate particles each includingmanganese are not particularly limited.

In the case of manganese-attached barium titanate, the attaching may beperformed by adding a manganese component to commercially available orsynthesized barium titanate particles in a downstream step. An additionmethod for the manganese component is not limited. However, it isdesired that the manganese component be uniformly attached to thesurface of barium titanate. In the viewpoint, the most preferredaddition method is a spray-drying method. The spray-drying method isalso preferred from the viewpoints that the method allows producinggranulating powder by adding a binder concomitantly with the attachingof the manganese component and that the method allows making theparticle diameter more uniform.

In the case of barium titanate in which manganese is dissolved as asolid solution, a barium titanate precursor in which a manganesecomponent is previously incorporated may be crystallized. For example,an equimolar mixture of a barium compound and a titanium compound isprepared, and a desired amount of a manganese component is then added tothe mixture. Subsequently, the mixture is calcined at about 1,000° C. toobtain barium titanate particles in each of which the manganesecomponent is dissolved as a solid solution. Also in this case, amanufacturing method for the granulating powder is not particularlylimited. However, a spray-drying method is preferred from the viewpointthat the method allows making the particle diameter more uniform.

Examples of the binder which may be used in granulation includepolyvinyl alcohol (PVA), polyvinyl butyral (PVB), and an acrylic resin.The amount of the binder added is preferably 1% by mass to 10% by mass,more preferably 2% by mass to 5% by mass from the viewpoint of anincrease in density of a molded article.

Examples of the barium compound which may be used in the production ofthe barium titanate particles each including manganese include bariumcarbonate, barium oxalate, barium oxide, barium acetate, barium nitrate,barium aluminate, and various barium alkoxides.

Examples of the titanium compound which may be used for the bariumtitanate particles each including manganese include titanium oxide.

Examples of the manganese component which may be used for the bariumtitanate particles each including manganese include manganese compoundssuch as manganese oxide, manganese dioxide, manganese acetate, andmanganese carbonate.

The above-mentioned manufacturing method includes sintering a mixtureprepared by adding the titanium oxide particles to the granulatingpowder. In other words, the mixture is in a state in which the abundanceof titanium is larger than that of barium. However, as a main componentobtained by sintering the mixture is barium titanate (Ba:Ti=1:1), thetitanium in excess is precipitated as Ba₄Ti₁₂O₂₇ particles or Ba₆Ti₁₇O₄₀particles, in which the abundance of Ti is larger than that of Ba, inthe grain boundary. Here, the average particle diameter of the titaniumoxide particles is 100 nm or less. The titanium oxide particles eachhave an average particle diameter of 100 nm or less, and hence showexcellent dispersibility with the mixture B and are mixed moreuniformly. By the above-mentioned mechanism, such piezoelectric ceramicsis capable of keeping Mn in the crystal particles to satisfy both thepiezoelectric performance and the mechanical quality factor. Theaddition amount of the titanium oxide particles is preferably 0.02% bymass or more and 1.5% by mass or less. In other words, the manufacturingmethod allows the Ba₄Ti₁₂O₂₇ particles or the Ba₆Ti₁₇O₄₀ particles to beprecipitated in the grain boundary in a relatively simple manner.

Hereinafter, a piezoelectric element using the piezoelectric ceramics ofthe present invention is described.

The piezoelectric element according to the present invention is apiezoelectric element including at least a first electrode, apiezoelectric ceramics, and a second electrode, and the piezoelectricceramics is the above-mentioned piezoelectric ceramics.

The first electrode and the second electrode are each formed of aconductive layer having a thickness of about 5 nm to 2,000 nm. Thematerial for the conductive layer is not particularly limited, and maybe a material which is typically used in a piezoelectric element.Examples of such material include metals such as Ti, Pt, Ta, Ir, Sr, In,Sn, Au, Al, Fe, Cr, Ni, Pd, Ag, and Cu, and oxides of these metals. Eachof the first electrode and the second electrode may be formed of onekind of those materials, or may be obtained by laminating two or morekinds thereof. The first electrode and the second electrode may beformed of different materials, respectively.

A manufacturing method for the first electrode and the second electrodeis not limited. The first electrode and the second electrode may beformed by baking a metal paste or by sputtering, vapor deposition, orthe like. In addition, both the first electrode and the second electrodemay be patterned in desired shapes for use.

FIGS. 1A and 1B are each a schematic view illustrating an embodiment ofthe construction of a liquid discharge head of the present invention. Asillustrated in FIGS. 1A and 1B, the liquid discharge head of the presentinvention is a liquid discharge head including a piezoelectric element101 of the present invention. The piezoelectric element 101 is apiezoelectric element including at least a first electrode 1011, apiezoelectric ceramics 1012, and a second electrode 1013. Thepiezoelectric ceramics 1012 is patterned as required as illustrated inFIG. 1B.

FIG. 1B is a schematic view of the liquid discharge head. The liquiddischarge head includes discharge ports 105, individual liquid chambers102, communicating holes 106 for connecting the individual liquidchambers 102 and the discharge ports 105, liquid chamber partition walls104, a common liquid chamber 107, a diaphragm 103, and the piezoelectricelements 101. Each of the piezoelectric elements 101, which is of arectangular shape in the figure, may be of a shape except therectangular shape such as an elliptical shape, a circular shape, or aparallelogram shape. In general, the piezoelectric ceramics 1012 areeach of a shape in conformity with the shape of the individual liquidchamber 102.

The vicinity of the piezoelectric element 101 in the liquid dischargehead of the present invention is described in detail with reference toFIG. 1A. FIG. 1A is a sectional view of the piezoelectric element in thewidth direction of the liquid discharge head illustrated in FIG. 1B. Thesectional shape of the piezoelectric element 101, which is illustratedin a rectangular shape, may be a trapezoidal shape or a reversetrapezoidal shape.

In the figure, the first electrode 1011 is used as the lower electrode,and the second electrode 1013 is used as the upper electrode. However,the arrangement of the first electrode 1011 and the second electrode1013 is not limited to the foregoing. For example, the first electrode1011 may be used as the lower electrode, or may be used as the upperelectrode. Similarly, the second electrode 1013 may be used as the upperelectrode, or may be used as the lower electrode. In addition, a bufferlayer 108 may be present between the diaphragm 103 and the lowerelectrode.

Note that, those differences in name are caused by a manufacturingmethod for the device and an effect of the present invention can beobtained in any case.

In the liquid discharge head, the diaphragm 103 vertically fluctuatesowing to the expansion and contraction of the piezoelectric ceramics1012 to apply a pressure to liquid in the individual liquid chamber 102.As a result, the liquid is discharged from the discharge port 105. Theliquid discharge head of the present invention can be used in a printerapplication or the manufacture of an electronic device.

The diaphragm 103 has a thickness of 1.0 μm or more and 15 μm or less,preferably 1.5 μm or more and 8 μm or less. A material for thediaphragm, which is not limited, is preferably Si. Si for the diaphragmmay be doped with B or P. In addition, the buffer layer and theelectrode layer on the diaphragm may serve as part of the diaphragm.

The buffer layer 108 has a thickness of 5 nm or more and 300 nm or less,preferably 10 nm or more and 200 nm or less.

The size of the discharge port 105 is 5 μm or more and 40 μm or less interms of a circle-equivalent diameter. The shape of the discharge port105 may be a circular shape, or may be a star shape, a square shape, ora triangular shape.

Next, an ultrasonic motor using the piezoelectric element of the presentinvention is described.

FIGS. 2A and 2B are schematic views illustrating an embodiment of theconstruction of the ultrasonic motor of the present invention.

FIG. 2A illustrates an ultrasonic motor in which the piezoelectricelement of the present invention is formed of a single plate. Theultrasonic motor includes a vibrator 201, a rotor 202 brought intocontact with the sliding surface of the vibrator 201 by virtue of apressure applied from a pressurizing spring (not shown), and an outputaxis 203 provided so as to be integral with the rotor 202. The vibrator201 is formed of a metal elastic ring 2011, a piezoelectric element 2012of the present invention, and an organic adhesive 2013 for bonding thepiezoelectric element 2012 to the elastic ring 2011 (such as an epoxy-or cyanoacrylate-based adhesive). The piezoelectric element 2012 of thepresent invention is formed of a piezoelectric ceramics interposedbetween a first electrode (not shown) and a second electrode (notshown).

The application of two alternating voltages different from each other inphase by π/2 to the piezoelectric element of the present inventionresults in the generation of a bending travelling wave in the vibrator201, and hence each point on the sliding surface of the vibrator 201undergoes an elliptical motion. When the rotor 202 is brought intopressure contact with the sliding surface of the vibrator 201, the rotor202 receives a frictional force from the vibrator 201 to rotate in thedirection opposite to the bending travelling wave. A body to be driven(not shown) is joined to the output axis 203, and is driven by therotary force of the rotor 202.

The application of a voltage to the piezoelectric ceramics results inthe expansion and contraction of the piezoelectric ceramics due to apiezoelectric transverse effect. When an elastic body such as a metal isjoined to the piezoelectric element, the elastic body is bent by theexpansion and contraction of the piezoelectric ceramics. The ultrasonicmotor of the kind described here utilizes the principle.

Next, an ultrasonic motor including a piezoelectric element having alaminated structure is illustrated in FIG. 2B. A vibrator 204 is formedof a laminated piezoelectric element 2042 interposed between tubularmetal elastic bodies 2041. The laminated piezoelectric element 2042 isan element formed of multiple laminated piezoelectric ceramics (notshown), and includes a first electrode and a second electrode on itsouter surface of lamination, and inner electrodes on its inner surfaceof lamination. The metal elastic bodies 2041 are fastened with bolts sothat the piezoelectric element 2042 may be interposed between and fixedby the bodies. Thus, the vibrator 204 is formed.

The application of alternating voltages different from each other inphase to the piezoelectric element 2042 causes the vibrator 204 toexcite two vibrations orthogonal to each other. The two vibrations aresynthesized to form a circular vibration for driving the tip portion ofthe vibrator 204. Note that, a constricted circumferential groove isformed in the upper portion of the vibrator 204 to enlarge thedisplacement of the vibration for driving.

A rotor 205 is brought into contact with the vibrator 204 under apressure from a spring 206 for pressurization to obtain a frictionalforce for driving. The rotor 205 is rotatably supported by a bearing.

Next, a dust removal device using the piezoelectric element of thepresent invention is described.

FIGS. 3A and 3B are schematic diagrams illustrating an embodiment of thedust removal device of the present invention.

A dust removal device 310 includes a plate-like piezoelectric element330 and a vibration plate 320. The material of the vibration plate 320is not limited. In the case where the dust removal device 310 is usedfor an optical device, a transparent material or a light reflectivematerial can be used as the material of the vibration plate 320.

FIGS. 4A to 4C are schematic diagrams illustrating a construction of thepiezoelectric element 330 illustrated in FIGS. 3A and 3B. FIGS. 4A and4C illustrate a front surface construction and a rear surfaceconstruction of the piezoelectric element 330, respectively. FIG. 4Billustrates a side surface construction. As illustrated in FIGS. 4A to4C, the piezoelectric element 330 includes piezoelectric ceramics 331, afirst electrode 332, and a second electrode 333. The first electrode 332and the second electrode 333 are disposed so as to be opposed to theplate surfaces of the piezoelectric ceramics 331. In FIG. 4C, the frontsurface of the piezoelectric element 330 on which the first electrode332 is disposed is referred to as a first electrode surface 336. In FIG.4A, the front surface of the piezoelectric element 330 on which thesecond electrode 333 is disposed is referred to as a second electrodesurface 337.

Here, the electrode surface in the present invention means a surface ofthe piezoelectric element on which the electrode is disposed. Forinstance, as illustrated in FIGS. 4A to 4C, the first electrode 332 mayextend around to the second electrode surface 337.

As illustrated in FIGS. 3A and 3B, as for the piezoelectric element 330and the vibration plate 320, the plate surface of the vibration plate320 is fixed to the first electrode surface 336 of the piezoelectricelement 330. When the piezoelectric element 330 is driven, a stress isgenerated between the piezoelectric element 330 and the vibration plate320, so that out-of-plane vibration is generated in the vibration plate.The dust removal device 310 of the present invention is a device thatremoves foreign matters such as dust adhering to the surface of thevibration plate 320 by the out-of-plane vibration of the vibration plate320. The out-of-plane vibration means elastic vibration in which thevibration plate moves in the optical axis direction, namely in thethickness direction of the vibration plate.

FIG. 5 is schematic diagram illustrating a vibration principle of thedust removal device 310 of the present invention. FIG. 5 aboveillustrates a state in which alternating electric fields having the samephase are applied to a pair of left and right piezoelectric elements 330so that the out-of-plane vibration is generated in the vibration plate320. The polarization direction of the piezoelectric ceramics formingthe pair of left and right piezoelectric elements 330 is the same as thethickness direction of the piezoelectric elements 330, and the dustremoval device 310 is driven by the seventh vibrational mode. FIG. 5below illustrates a state in which alternating voltages having oppositephases by 180 degrees are applied to the pair of left and rightpiezoelectric elements 330 so that the out-of-plane vibration isgenerated in the vibration plate 320. The dust removal device 310 isdriven by the sixth vibrational mode. The dust removal device 310 of thepresent invention is a device that can effectively remove dust adheringto the surface of the vibration plate by using at least two vibrationalmodes selectively.

As described above, the piezoelectric element of the present inventionis suitably applicable to the liquid discharge head, the ultrasonicmotor, and the dust removal device.

By using the lead-free piezoelectric ceramics containing at least onecompound selected from Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ of the presentinvention, it is possible to provide the liquid discharge head havingthe same or higher nozzle density and discharge force than the casewhere the piezoelectric ceramics containing lead is used.

By using the lead-free piezoelectric ceramics containing at least onecompound selected from Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ of the presentinvention, it is possible to provide the ultrasonic motor having thesame or higher driving force and durability than the case where thepiezoelectric ceramics containing lead is used.

By using the lead-free piezoelectric ceramics containing at least onecompound selected from Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ of the presentinvention, it is possible to provide the dust removal device having thesame or higher dust-removing efficiency than the case where thepiezoelectric ceramics containing lead is used.

The piezoelectric ceramics of the present invention can be used indevices such as an ultrasonic vibrator, a piezoelectric actuator, apiezoelectric sensor, a ferroelectric memory, and the like in additionto the liquid discharge head and the motor.

As described above, the piezoelectric element of the present inventionis suitably used in the liquid discharge head and the ultrasonic motor.The liquid discharge head includes a lead-free piezoelectric elementcontaining barium titanate as a principle component. Thus, the head canbe provided as one having the same or higher nozzle density anddischarge force than those of a lead-based piezoelectric element. Inaddition, the ultrasonic motor may include a lead-free piezoelectricelement containing barium titanium as a principle component. Thus, themotor can be provided as one having the same or higher driving force anddurability than those of the lead-based piezoelectric element.

The piezoelectric ceramics of the present invention can be used indevices such as an ultrasonic vibrator, a piezoelectric actuator, and apiezoelectric sensor, and the like in addition to the liquid dischargehead and the motor.

EXAMPLES

Hereinafter, the present invention is described more specifically by wayof examples. However, the present invention is not limited by thefollowing examples.

Example 1 Manufacturing Method 1 for Ceramics

Barium carbonate, titanium oxide, and manganese oxide were used as rawmaterials, and weighted to give a 1:1 mole ratio of Ba to Ti whilegiving 0.12% by mass of manganese added with respect to the total massof barium oxide and titanium oxide in terms of metals. Then, these rawmaterials were mixed. The resulting mixed powder was calcined at 900° C.to 1,100° C. for 2 to 5 hours.

Subsequently, 3% by mass of PVA as a binder was added to the calcinedpowder and the resulting mixture was spray-dried to give granulatingpowder. Then, 0.9% by mass of Ba₄Ti₁₂O₂₇ was added to and mixed with thegranulating powder.

Next, the obtained powder was filled in a die and then compressed toform a compact. The resulting compact was sintered at 1,300° C. to1,400° C. for 2 to 6 hours to obtain a ceramics. Here, a heat-up ratewas set to 10° C./minute and the thermocouple of an electric furnace wasadjusted so as to prevent an overshoot of 10° C. or more from asintering temperature.

The resulting sintered body was ground to a thickness of 1 mm. Afterthat, the sintered body was subjected to heat treatment in the air at450° C. to 1,100° C. for 1 to 3 hours to remove organic components fromthe surface of the sintered body.

Example 2 Manufacturing Method 2 for Ceramics

Barium carbonate, titanium oxide, and manganese oxide were used as rawmaterials, and weighted to give a 1:1 mole ratio of Ba to Ti whilegiving 0.12% by mass of manganese added with respect to the total massof barium oxide and titanium oxide in terms of metals. Then, these rawmaterials were mixed. The resulting mixed powder was calcined at 900° C.to 1,100° C. for 2 to 5 hours.

Subsequently, 3% by mass of PVA as a binder was added to the calcinedpowder and the resulting mixture was spray-dried to give granulatingpowder. Then, 0.85% by mass of Ba₆Ti₁₇O₄₀ was added to and mixed withthe granulating powder.

Next, the obtained powder was filled in a die and then compressed toform a compact. The resulting compact was sintered at 1,300° C. to1,400° C. for 2 to 6 hours to obtain a ceramics. Here, a heat-up ratewas set to 10° C./minute and the thermocouple of an electric furnace wasadjusted so as to prevent an overshoot of 10° C. or more from asintering temperature.

The resulting sintered body was ground to a thickness of 1 mm. Afterthat, the sintered body was subjected to heat treatment in the air at450° C. to 1,100° C. for 1 to 3 hours to remove organic components fromthe surface of the sintered body.

Example 3 Manufacturing Method 3 for Ceramics

Barium carbonate, titanium oxide, and manganese oxide were used as rawmaterials, and weighted to give a 1:1 mole ratio of Ba to Ti whilegiving 0.12% by mass of manganese added with respect to the total massof barium oxide and titanium oxide in terms of metals. Then, these rawmaterials were mixed. The resulting mixed powder was calcined at 900° C.to 1,100° C. for 2 to 5 hours.

Subsequently, 3% by mass of PVA as a binder was added to the calcinedpowder and the resulting mixture was spray-dried to give granulatingpowder. Then, 0.45% by mass each of Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ was addedto and mixed with the granulating powder.

Next, the obtained powder was filled in a die and then compressed toform a compact. The resulting compact was sintered at 1,300° C. to1,400° C. for 2 to 6 hours to obtain a ceramics. A heat-up rate was setto 10° C./minute and the thermocouple of an electric furnace wasadjusted so as to prevent an overshoot of 10° C. or more from asintering temperature.

The resulting sintered body was ground to a thickness of 1 mm. Thesintered body was subjected to heat treatment in the air at 450° C. to1,100° C. for 1 to 3 hours to remove organic components from the surfaceof the sintered body.

Example 4 to Example 10 Manufacturing Method 4 for Ceramics

Barium carbonate, titanium oxide, and manganese oxide were used as rawmaterials, and weighted to give a 1:1 mole ratio of Ba to Ti whilegiving an amount of manganese added as shown in Table 1. Then, these rawmaterials were mixed. The resulting mixed powder was calcined at 900° C.to 1,100° C. for 2 to 5 hours.

Subsequently, 3% by mass of PVA as a binder was added to the calcinedpowder and the resulting mixture was spray-dried to give granulatingpowder. Then, the granulating powder was mixed with titanium oxide(TiO₂) of 10 nm to 30 nm in average particle diameter and the resultingpowder was filled in a die, followed by compression to form a compact.

Next, the resulting compact was sintered at 1,300° C. to 1,450° C. for 2to 6 hours to obtain a ceramics. A heat-up rate was set to 10° C./minuteand the thermocouple of an electric furnace was adjusted so as toprevent an overshoot of 10° C. or more from a sintering temperature.

The resulting sintered body was ground to a thickness of 1 mm. Thesintered body was subjected to heat treatment in the air at 450° C. to1,100° C. for 1 to 3 hours to remove organic components from the surfaceof the sintered body.

Comparative Example 1 Manufacturing Method 5 for Ceramics

Barium carbonate, titanium oxide, and manganese oxide were used as rawmaterials, and weighted to give a 1:1 mole ratio of Ba to Ti whilegiving 0.12% by mass of manganese added with respect to the total massof barium oxide and titanium oxide in terms of metals. Then, these rawmaterials were mixed. The resulting mixed powder was calcined at 900° C.to 1,100° C. for 2 to 5 hours.

Subsequently, 3% by mass of PVA as a binder was added to the calcinedpowder and the resulting mixture was spray-dried to give granulatingpowder. The granulating powder was filled in a die, followed bycompression to form a compact.

The resulting compact was sintered at 1,300° C. to 1,400° C. for 2 to 6hours to obtain a ceramics. A heat-up rate was set to 10° C./minute andthe thermocouple of an electric furnace was adjusted so as to prevent anovershoot of 10° C. or more from a sintering temperature.

The resulting sintered body was ground to a thickness of 1 mm. Thesintered body was subjected to heat treatment in the air at 450° C. to1,100° C. for 1 to 3 hours to remove organic components from the surfaceof the sintered body.

Table 1 shows manufacturing conditions of the piezoelectric ceramics ofExamples 1 to 10. In the table, the item “Mn amount” represents theweighed amount of manganese.

TABLE 1 Manufacturing conditions of piezoelectric ceramics AdditiveSintering Manufacturing Mn amount amount temperature method (% by mass)Additive (% by mass) (° C.) Example 1 1 0.12 Ba₄Ti₁₂O₂₇ 0.9 1,380Example 2 2 0.12 Ba₆Ti₁₇O₄₀ 0.85 1,380 Example 3 3 0.12 Ba₄Ti₁₂O₂₇ 0.91,380 Ba₆Ti₁₇O₄₀ Example 4 4 0.04 TiO₂ 1 1,380 Example 5 4 0.12 TiO₂ 0.91,380 Example 6 4 0.2 TiO₂ 0.4 1,380 Example 7 4 0.12 TiO₂ 0.05 1,300Example 8 4 0.12 TiO₂ 0.4 1,330 Example 9 4 0.12 TiO₂ 1 1,420 Example 104 0.12 TiO₂ 2 1,400 Comparative 5 0.12 None 0 1,380 Example 1

(Structural Evaluation of Piezoelectric Ceramics)

The structures of crystal particles and grain boundary of the obtainedpiezoelectric ceramics were evaluated using a transmission electronmicroscope (TEM).

First, the crystal structure of crystal particles in each piezoelectricceramics was evaluated using an electron diffraction image. In Examples1 to 10 and Comparative Example 1, the crystal particles were eachformed of BaTiO₃ having an Mn-containing perovskite structure. The Mn inthe crystal particles was determined using an electron probe microanalyzer (referred to as EPMA). In addition, the crystal particlediameter was evaluated using a scanning electron microscope.

Further, the composition of the whole piezoelectric ceramics wasevaluated by X-ray fluorescence analysis (XRF).

The piezoelectric ceramics was evaluated for grain boundary parts.Specifically, the percentage of the grain boundary parts in thepiezoelectric ceramics, the crystal structure in the grain boundary, thepresence or absence of Mn in the crystals, and the amount of Mn in thegrain boundary were determined.

A procedure for preparing a sample for observation of piezoelectricceramics using a transmission electron microscope is described. First, ametal or carbon film was laminated on the surface of the piezoelectricceramics which was polished to a mirror-finished surface. Such coatingwas provided for preventing electric charges from being accumulated onthe surface of the piezoelectric ceramics during the process formanufacturing a TEM thin sample. Then, a thin sample of approximately 1μm in thickness by 10 μm in width by 5 μm in length was cut out from thesurface of the piezoelectric ceramics using a focused ion beam. Thesample was attached to a grid for TEM observation. The sample wasirradiated with a focused ion beam in parallel with the longitudinaldirection of the sample so that the sample had a thickness of about 100nm over an area of approximately 5 μm in length. The transmissionelectron microscope observation was carried out by irradiating thesample (1 μm in thickness by 10 μm in width by 5 μm in length) with anelectron beam from the thickness direction thereof.

An electron diffraction image of the grain boundary was acquired usingthe selected-area diffraction method. Simultaneously, a known bariumtitanate crystal particle part (BaTiO₃) was observed under the sameconditions to define a camera constant. Lattice spacing was calculatedfrom the resulting diffraction image of the grain boundary part. Theelectronic diffraction image observation was carried out while theinclination angle of the sample was arbitrarily changed to give severaldifferent diffraction images from the same point of the grain boundary.The lattice spacing of each diffraction image was calculated andcompared with the known literature data to specify the crystal structureof the grain boundary. The composition of the grain boundary part wasanalyzed by the STEM-EDX method to calculate the concentration of Mn inthe grain boundary part. The “STEM-EDX” is a technique for measuring, byenergy dispersive X-ray spectroscopy (EDX), the intensity of X-rayfluorescence at any place on a same image observed by scan transmissionelectron microscopy (STEM).

Physical properties of crystal particles and grain boundaries of theobtained piezoelectric ceramics are listed in Table 2.

(Evaluation of content of physical properties of grain boundary)

-   -   A: Only Ba₄Ti₁₂O₂₇ was contained.    -   B: Only Ba₆Ti₁₇O₄₀ was contained.    -   C: Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ were contained.    -   x: None of the crystal structures of Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀        was confirmed.

(Evaluation of Presence or Absence of Mn of Physical Properties of GrainBoundary)

o: Mn was present in the crystals contained in the grain boundary.x: Mn was not present in the crystals contained in the grain boundary.

Further, the results of the composition analysis by the XRF (but omittedin the table) revealed that a mole ratio of Ba to Ti was 1.0:1.0 in eachof Examples 1 to 10 and Comparative Example 1.

TABLE 2 Physical properties of crystal particles and grain boundaryPhysical properties of grain boundary Physical properties of Graincrystal particles boundary Presence or Particle Mn amount ratio absenceof Mn amount diameter (μm) (% by mass) (% by area) Content Mn (% bymass) Example 1 110 0.12 0.9 A ∘ 1.2 Example 2 90 0.12 0.85 B ∘ 1.7Example 3 100 0.12 0.9 C ∘ 1.3 Example 4 150 0.04 1 C x 0.4 Example 5100 0.12 0.9 C ∘ 1.5 Example 6 50 0.2 0.4 C ∘ 3 Example 7 10 0.12 0.05 C∘ 1.2 Example 8 50 0.12 0.4 C ∘ 1.2 Example 9 150 0.12 1 C ∘ 1.3 Example10 200 0.12 2 C ∘ 1.2 Comparative 100 0.1 0.9 x x 1 Example 1

(Grain Boundary Ratio)

A grain boundary ratio represents a percentage (% by area) of at leastone compound selected from Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ contained in thegrain boundary.

As a result of the surface image observation by SEM, it was found thatsub-particles were observed with a contrast different from that of thecrystal particles. Based on the results of the SEM observation, ananalysis using the technique described below was performed to determinea ratio of at least one compound selected from Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀contained in the grain boundary to the whole piezoelectric ceramics. Inother words, an SEM image of the surface of the piezoelectric ceramicswas observed and represented in binary based on a difference in contrastbetween the crystal particle part and the sub-particle part to measurethe area of each of the both parts. For simplifying the measurement, theareas were calculated for every set of 10 photographed SEM images. Theabove-mentioned analysis was performed on an area which was consideredto be sufficiently large for distribution of the sub-particles in thepiezoelectric ceramics. By comparing the total of the areas of thesub-particles and the total of the areas of the crystal particlesobtained by the above-mentioned analysis, the content rate (% by area)of the sub-particles to the piezoelectric ceramics was calculated.

FIG. 8B is an electron diffraction image of Example 5 obtained by theTEM selected-area diffraction method. FIG. 8A shows a [100] incidentelectron diffraction pattern of Ba₄Ti₁₂O₂₇ calculated from literaturedata. By comparing their lattice spacings, it was confirmed that thesub-particles contained Ba₄Ti₁₂O₂₇. Similarly, it was also confirmed ineach of Examples 1, 3, 4, and 6 to 10.

Table 3 shows results of the comparison between the lattice spacingobtained from the above-mentioned electron diffraction image observedusing the selected-area diffraction method and the lattice spacingobtained from the known literature data of Ba₄Ti₁₂O₂₇. As is evidentfrom the following table, Ba₄Ti₁₂O₂₇ is present in the piezoelectricceramics of the present invention.

TABLE 3 Comparison of spacing ([100] incident electron diffraction imageof Ba₄Ti₁₂O₂₇) Spacing d (nm) Experimental value Literature value A: (00 1) 0.949 0.937 B: (0 2 1) 0.583 0.572 C: (0 2 0) 0.495 0.488

Further, FIG. 9B is an electron diffraction image of the grain boundarypart in the piezoelectric ceramics of Example 5 obtained by the TEMselected-area diffraction method. FIG. 9A shows a [011] incidentelectron diffraction pattern of Ba₆Ti₁₇O₄₀ calculated from literaturedata. By comparing their lattice spacings, it was confirmed that thesub-particles contained Ba₆Ti₁₇O₄₀. Similarly, it was also confirmed ineach of Examples 2 to 4 and 6 to 10.

Table 4 shows results of the comparison between the lattice spacingobtained from the above-mentioned electron diffraction image observed bythe selected-area diffraction method and the lattice spacing obtainedfrom the known literature data of Ba₆Ti₁₇O₄₀.

TABLE 4 Comparison of spacing ([011] incident electron diffraction imageof Ba₆Ti₁₇O₄₀) Observed spacing Literature spacing Miller indices value(nm) value (nm) A: (−1 −1 1) 0.800 0.814 B: (−1 1 −1) 0.724 0.737 C: (02 −2) 0.623 0.631

In Comparative Example 1, any crystal structure of Ba₄Ti₁₂O₂₇ andBa₆Ti₁₇O₄₀ was not found in the grain boundary. Thus, it is found thatthe amount of Mn in the crystal particles is smaller than the weighedamount of Mn. On the other hand, in Examples 1 to 10, the amount of Mnin the crystal particles was substantially equal to the weighed amountof Mn. This is probably because Mn was efficiently incorporated intocrystal particles as a result of including at least one of Ba₄Ti₁₂O₂₇and Ba₆Ti₁₇O₄₀ in the grain boundary.

In addition, the amount of Mn in the grain boundary part in each ofExamples 1 to 10 was measured. Specifically, grain boundaries weremeasured at multiple points by combining the crystal structure obtainedby the selected-area diffraction method with the energy dispersivespectroscopy. As a result, only in Example 4, Mn was found in none ofBa₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀. Further, in Examples 3 and 5 to 10, an areawhere the crystal structure was Ba₄Ti₁₂O₂₇ found to contain Mnapproximately 1% by mass more than Ba₆Ti₁₇O₄₀ in average. Therefore, forexample, by adding the Ba₄Ti₁₂O₂₇ particles to the granulating powder,the precipitation of manganese out of the crystal particles of thepiezoelectric ceramics was able to be effectively prevented bymanufacturing the piezoelectric ceramics in which the grain boundarieswere occupied by only Ba₄Ti₁₂O₂₇.

(Evaluation of Piezoelectric Properties of Ceramics)

Gold electrodes were formed on both the front and back sides of themanufactured piezoelectric ceramics by the DC sputtering method toevaluate the piezoelectric properties of the piezoelectric ceramics.Then, the electrode-mounted ceramics was cut into a rectangle (stripceramics) of 10 mm by 2.5 mm by 1 mm in size.

The resulting strip ceramics was polarized. The polarization wasperformed under the conditions of: a polarization voltage of 1 kV DC anda voltage-application time of 30 minutes at a temperature of 100° C.

A piezoelectric constant was determined using the polarized stripceramics. Specifically, the frequency dependency of impedance of theceramics sample was determined using an impedance analyzer (trade name:4294A, manufactured by Agilent Co., Ltd.). Then, the piezoelectricconstant d₃₁ (pm/V) and the mechanical quality factor Q_(m) werecalculated from the observed resonance frequency and anti-resonancefrequency. The piezoelectric constant d₃₁ has a negative value, and alarger absolute value thereof means higher piezoelectric performance. Inaddition, a larger absolute value of the mechanical quality factor Q_(m)means a smaller loss in resonance vibration of the resonator.

Results of the evaluation of the piezoelectric properties are listed inTable 5.

TABLE 5 Piezoelectric properties Piezoelectric constant d₃₁ Mechanical(pm/V) quality factor Q_(m) Example 1 107 1,320 Example 2 106 1,210Example 4 110 520 Example 5 118 1,290 Example 6 106 1,840 Example 10 1141,260 Comparative 95 440 Example 1

As is evident from Table 5, it is found that including at least one ofBa₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ in the grain boundary can improve both thepiezoelectric constant d₃₁ and the mechanical quality factor Q_(m).

(Liquid Discharge Head According to Example 1)

Using the same piezoelectric ceramics as that of Example 1, a liquiddischarge head illustrated in FIGS. 1A and 1B was prepared. Inkdischarge from the liquid discharge head in response to input electricsignals was confirmed.

(Ultrasonic Motor According to Example 1)

Using the same piezoelectric ceramics as that of Example 1, anultrasonic motor illustrated in FIGS. 2A and 2B were prepared. Therotary behavior of the motor in response to application of analternating voltage was confirmed.

(Dust Removal Device According to Example 1)

Using the same piezoelectric ceramics as that of Example 1, a dustremoval device illustrated in FIGS. 3A and 3B were prepared. When analternating voltage was applied after bedashing plastic beads, asatisfactory dust-removing rate was confirmed.

INDUSTRIAL APPLICABILITY

The piezoelectric ceramics of the present invention has both ofsatisfactory piezoelectric performance and a satisfactory mechanicalquality factor. In addition, the piezoelectric ceramics of the presentinvention is environmentally clean. Thus, the piezoelectric ceramics canbe used in a device that utilizes a large amount of piezoelectricceramics, such as a liquid discharge head, an ultrasonic motor, and apiezoelectric element.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2010-285742, filed Dec. 22, 2010, which is hereby incorporated byreference herein in its entirety.

REFERENCE SIGNS LIST

-   101 piezoelectric element-   102 individual liquid chamber-   103 vibration plate-   104 liquid chamber partition wall-   105 discharge port-   106 communicating hole-   107 common liquid chamber-   108 buffer layer-   1011 first electrode-   1012 piezoelectric ceramics-   1013 second electrode-   201 vibrator-   202 rotor-   203 output axis-   204 vibrator-   205 rotor-   206 spring-   2011 elastic ring-   2012 piezoelectric element-   2013 organic adhesive-   2041 metal elastic body-   2042 laminated piezoelectric element-   310 dust removal device-   330 piezoelectric element-   320 vibration plate-   331 piezoelectric ceramics-   332 first electrode-   333 second electrode-   336 first electrode surface-   337 second electrode surface-   401 barium titanate crystal particle-   402 boundary between crystal particles-   403 triple point-   404 sub-particle present on boundary between crystal particles-   405 sub-particle present on boundary between crystal particles and    at triple point-   406 sub-particle present at triple point-   501 barium titanate crystal particle-   502 sub-particle-   503 barium titanate crystal particle-   504 sub-particle

1. A piezoelectric ceramics, comprising: crystal particles; and a grainboundary between the crystal particles, wherein: the crystal particlescomprise barium titanate having a perovskite-type structure andmanganese at 0.04% by mass or more and 0.20% by mass or less in terms ofa metal with respect to the barium titanate, and the grain boundarycomprises at least one compound selected from the group consisting ofBa₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀.
 2. The piezoelectric ceramics according toclaim 1, wherein a ratio of the at least one compound selected from thegroup consisting of Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ in the grain boundary whenobserved on one of a surface and a cross-section of the piezoelectricceramics is 0.05% by area or more and 1% by area or less with respect toa total area of one of the surface and the cross-section of thepiezoelectric ceramics.
 3. The piezoelectric ceramics according to claim1, wherein: the grain boundary comprises one of Ba₄Ti₁₂O₂₇ andBa₆Ti₁₇O₄₀, and the Ba₄Ti₁₂O₂₇ and the Ba₆Ti₁₇O₄₀ both comprisemanganese.
 4. The piezoelectric ceramics according to claim 1, wherein:the grain boundary comprises Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀, and theBa₄Ti₁₂O₂₇ and the Ba₆Ti₁₇O₄₀ comprise manganese.
 5. The piezoelectricceramics according to claim 4, wherein a content ratio of manganese inthe Ba₄Ti₁₂O₂₇ is larger than a content ratio of manganese in theBa₆Ti₁₇O₄₀.
 6. The piezoelectric ceramics according to claim 1, whereina content of manganese in at least one compound selected from the groupconsisting of Ba₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀ in the grain boundary is 0.6% bymass or more and 2.8% by mass or less in terms of a metal with respectto the at least one compound selected from the group consisting ofBa₄Ti₁₂O₂₇ and Ba₆Ti₁₇O₄₀.
 7. A manufacturing method for a piezoelectricceramics, comprising at least: producing granulating powder by adding abinder to barium titanate particles comprising manganese at 0.04% bymass or more and 0.20% by mass or less in terms of a metal; andsintering a mixture prepared by adding at least one compound selectedfrom the group consisting of Ba₄Ti₁₂O₂₇ particles and Ba₆Ti₁₇O₄₀particles to the granulating powder.
 8. A manufacturing method for apiezoelectric ceramics, comprising at least: producing granulatingpowder by adding a binder to barium titanate particles comprisingmanganese at 0.04% by mass or more and 0.20% by mass or less in terms ofa metal; and sintering a mixture prepared by adding titanium oxideparticles having an average particle diameter of 100 nm or less to thegranulating powder.
 9. A piezoelectric element, comprising at least: afirst electrode; a piezoelectric ceramics; and a second electrode,wherein the piezoelectric ceramics comprises the piezoelectric ceramicsaccording to claim
 1. 10. A liquid discharge head, using thepiezoelectric element according to claim
 9. 11. An ultrasonic motor,using the piezoelectric element according to claim
 9. 12. A dust removaldevice, using the piezoelectric element according to claim 9.